JP3570750B2 - Hot wire anemometer - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a hot-wire anemometer, and more particularly to a hot-wire anemometer designed to improve low power consumption and noise resistance.
[0002]
[Prior art]
As shown in FIG. 5, a conventional hot wire anemometer using a bridge circuit uses, for example, a platinum wire 1 as a temperature-sensitive element, and forms a bridge circuit 2 with the platinum wire 1, resistors R1, R2 and a temperature-sensitive resistor R3. The bridge circuit 2 is balanced by the heating resistance value _RH at which the platinum wire 1 reaches a predetermined temperature. Then, the voltages on both sides of the bridge circuit 2 are connected to a pair of input terminals of the feedback amplifier 3 and fed back from the feedback amplifier 3 to the bridge circuit 2, causing the platinum wire 1 to generate heat and the bridge to be in a balanced state. Thus according to the voltage V _H across the platinum wire 1, it was measured by the following equation velocity U of the fluid passing through the platinum wire 1 (1).
^{_{V H 2 / R H = (}} a + b√U) (T P -T) ··· (1)
Here a, b are constants, the T _P temperature of the platinum wire 1, T is air temperature, the R _H is a heating resistance of the platinum wire. 4 square of the voltage V _H applied to the platinum wire 1 is proportional to the wind velocity U as is known from the equation. And incorporated into the bridge of the one side for the temperature compensation temperature sensing element R3 having the same temperature coefficient as the wind speed devices, heat dissipation rate also vary the wind temperature T, i.e., the platinum wire first temperature T _P and wind temperature T difference (T P _-T) is always set to be constant.
[0003]
[Problems to be solved by the invention]
However, the conventional hot-wire anemometer has a drawback that the current consumption is large because the feedback current is always supplied from the feedback amplifier 3 to the bridge circuit 2. Further, when the probe including the platinum wire 1 is operated away from the main body of the hot wire anemometer, it is necessary to connect the main body and the probe with a cable, and there is a disadvantage that the cable is susceptible to external noise such as induction. In order to make the hot-wire anemometer portable and operate using a battery as a power source, it is necessary to reduce the current consumption and make it less susceptible to external noise.
[0004]
The present invention has been made in view of such conventional problems, and has as its object to provide a hot-wire anemometer with low power consumption and less susceptibility to external noise.
[0005]
[Means for Solving the Problems]
The invention according to claim 1 of the present application is directed to a bridge circuit including a heating wire serving as a sensor on one side, a feedback amplifier that receives a voltage difference between both sides of the bridge circuit as input, and feeds back a differential amplified output to the bridge circuit. Feedback current intermittent means for intermittently applying the output of the feedback amplifier at a constant cycle to the bridge circuit, steady state discriminating means for outputting a pulse signal having a time width until the output from the feedback amplifier becomes a steady state, A time width detecting means for detecting a time width of an output from the discriminating means; and a wind speed converting means for converting a signal of the time width obtained by the time width detecting means into a wind speed value. .
[0006]
According to a second aspect of the present invention, there is provided a bridge circuit configured to include a heating wire serving as a sensor on one side, a feedback amplifier which receives a voltage difference between both sides of the bridge circuit as input, and feeds back a differential amplified output to the bridge circuit. Feedback current intermittent means for intermittently applying the output of the feedback amplifier at a constant cycle to the bridge circuit, discriminating means for outputting a signal obtained by discriminating a signal obtained from the feedback amplifier at a predetermined level, and time for output from the discriminating means. It is characterized by comprising a time width detecting means for detecting the width, and a wind speed converting means for converting a signal of the time width obtained from the time width detecting means into a wind speed value.
[0007]
[Action]
According to the present invention having such features, the bridge circuit including the sensor and the feedback amplifier are provided, and the feedback current value applied to the bridge circuit is interrupted by the feedback current interrupting means. According to the first aspect of the present invention, the time interval until the output of the feedback amplifier reaches a steady value is detected by the steady state determining means, and the output is converted into a wind speed value based on the time interval and output. According to the second aspect of the present invention, the output of the intermittent feedback amplifier is discriminated at a predetermined level by the discriminating means, and is converted into a wind speed value based on the time width of the pulse and output.
[0008]
【Example】
FIG. 1 is a block diagram showing an example of a hot-wire anemometer according to a first embodiment of the present invention. In this figure, the same parts as those of the above-described conventional example are denoted by the same reference numerals, and detailed description is omitted. In this embodiment, the bridge circuit 2 includes fixed resistors R1 and R2, a temperature-sensitive resistor R3 for temperature compensation, and a heating wire such as a sensor, for example, a platinum wire 1, as in the conventional example. The common connection point of the resistors R1 and R3 and the common connection point of the resistor R2 and the platinum wire 1 of the bridge circuit 2 are connected to the input terminal of the feedback amplifier 3. The output of the feedback amplifier 3 is connected to the steady state determination circuit 4 and further connected to the input terminal of the analog switch 5. The analog switch 5 has its input intermittently input by a clock signal from a clock oscillator 6, and its output is supplied as a feedback current to a common connection terminal of the resistors R1 and R2 of the bridge circuit 2. These blocks are housed in the probe of the hot wire anemometer. Here, the clock oscillator 6 and the analog switch 5 constitute feedback current interrupting means for interrupting the output of the feedback amplifier at a constant cycle and adding the output to the bridge circuit.
[0009]
The output of the steady state determination circuit 4 is supplied via a cable 7 to a waveform shaping circuit 8 in the main body of the hot wire anemometer. The waveform shaping circuit 8 removes a noise component which may be added by the cable 7 or the like, and reproduces a rectangular wave signal obtained from the steady state discriminating circuit 4. The output is supplied to the time width detector 9. . The time width detector 9 converts a rectangular wave signal of the waveform shaping circuit into a time signal, and includes a counter for counting a high-speed clock signal having a predetermined period. This time width signal is provided to the wind speed converter 10. The wind speed converter 10 converts a time width signal obtained from a previously calibrated relationship between the wind speed and the time width into a wind speed value, and outputs a wind speed value in response to the input of the time width. Consists of a table. The output of the wind speed converter 10 is output to the display 11.
[0010]
Next, the operation of this embodiment will be described with reference to a time chart. FIG. 2A shows a clock signal from the clock oscillator 6. During the period t _{1 to} t ₂ , t _{3 to} t _4, ... Where the output of the clock oscillator 6 is at the H level, the analog switch 5 is closed, and the output of the feedback amplifier 3 becomes a feedback signal as it is. The signal is input to the bridge circuit 2. Here since the rising time t ₁ of the clock signal is not energized in the platinum wire 1, it becomes possible to high level voltage at time t ₁ is applied, after a time of the time constant corresponding to the wind speed at that time Reach steady state. After reaching the steady state, the feedback current to the bridge circuit 3 is stopped at t ₂ , t _4, ... Where the clock signal from the clock oscillator 6 is inverted to L level, and the power supply is stopped . By intermittently driving the bridge circuit 2 in accordance with the clock cycle of the clock oscillator 6, the voltage output waveform of the feedback amplifier 3 changes as shown in FIG. Here, the steady state determination circuit 4 outputs a pulse having a time width until the steady state is reached, as shown in FIG. This signal is transmitted through the cable 7 to the main body of the wind speed sensor. Then, the waveform is shaped through the waveform shaping circuit 8, and the time is detected by the time width detector 9. Duration to reach this steady state between times t ₁ ~t ₅ becomes Ta. Also between times t ₆ ~t ₁₀ than this increases the wind speed has become a time width Tb up to this time reaches a steady state.
[0011]
The relationship between the time Ta, Tb... Until the steady state is reached and the wind speed U is represented by a substantially squared relationship as shown in FIG. This is data obtained as a result of the experiment, and the relationship between the wind speed and the time width T is stored in the ROM of the wind speed converter 10a. Therefore, by inputting the time widths Ta, Tb,..., The wind speed converter 10 converts the time widths into the wind speed values Ua, Ub at this time and outputs the values. This signal is displayed on the display 11. . By driving the bridge circuit 2 intermittently in this manner, the current consumption of the hot wire anemometer can be reduced. In this embodiment, a signal is transmitted from the probe to the hot-wire anemometer main body via the cable 7 using a rectangular pulse signal as shown in FIG. Therefore, even when noise is superimposed on this signal, if the waveform is shaped by the waveform shaping circuit 8, the influence of the noise can be extremely reduced.
[0012]
FIG. 4 is a block diagram showing a configuration of a hot-wire anemometer according to a second embodiment of the present invention. In this figure, the same parts as those in the first embodiment described above are denoted by the same reference numerals, and detailed description is omitted. In this embodiment, a discrimination circuit 20 is provided in place of the steady state determination circuit 4. The discrimination circuit 20 discriminates the output of the feedback amplifier 3 with a predetermined threshold value Vref, and outputs a rectangular wave signal. Other configurations are almost the same as those of the first embodiment. The signal converted into the rectangular wave is transmitted to the hot wire anemometer main body via the cable 7. A waveform shaping circuit 8 and a time width detector 9 are provided on the main body side, and a signal of a time width obtained at this time is supplied to a wind speed converter 21. The wind speed converter 21 is a memory for storing a conversion table for converting the time widths Tc, Td,... Obtained when the output of the feedback amplifier 3 is discriminated by a predetermined threshold value and the wind speed value into wind speed values. The data in this memory is obtained in advance by experiments. The data of the wind speed read out in accordance with the time width is input to the display 11.
[0013]
Next, the operation of this embodiment will be described. FIG. 2A shows the output of the clock oscillator as in the first embodiment, whereby the signal shown in FIG. 2D is output from the feedback amplifier 3. This signal is also the same as in FIG. 2B of the first embodiment. The output of the feedback amplifier is discriminated by a predetermined threshold value Vref, and is output as a signal shown in FIG. This signal is transmitted to the main body via the cable 7 as in the first embodiment, and the time widths Tc and Td obtained at this time are converted into wind speed values Uc and Ud by the wind speed converter 21 and displayed on the display 11. Is done. FIG. 3B is a graph showing the relationship between the wind speed U and the time width at this time. Also in this case, the wind speed U and the time width T are represented by a square curve as shown in FIG.
[0014]
In this case as well, since the bridge circuit is driven intermittently in the same manner, the current consumption can be reduced, and a hot-wire anemometer that is hardly affected by noise can be obtained. As shown in FIGS. 3A and 3B, since the time width and the wind speed are represented by a substantially squared relationship, the resolution is increased as compared with the conventional relationship between the voltage and the wind speed represented by Expression (1), and the wind speed is increased. Measurement accuracy can also be improved.
[0015]
In the first and second embodiments, if the duty ratio of the clock oscillator 6 is reduced, the power consumption can be further reduced, but the responsiveness of wind speed detection decreases. Therefore, by appropriately changing the duty ratio, it is possible to arbitrarily select a reduction in current consumption and an improvement in responsiveness.
[0016]
In the first and second embodiments, the feedback amplifier 3 is energized even when the analog switch is opened. However, the output of the analog switch 5 may be input to the steady state determination circuit 4 or the discrimination circuit 20. Further, the power supply of the feedback amplifier 3 may be turned on and off by the output of the clock oscillator 6. In this case, the probe can be configured without providing the analog switch 5.
[0017]
【The invention's effect】
As described in detail above, according to the first and second aspects of the present invention, since the bridge circuit is driven intermittently as compared with the conventional hot-wire anemometer, the current consumption can be greatly reduced. Further, even when the probe portion and the main body of the hot-wire anemometer are separated from each other and the cable connecting them is extended, the hot-wire anemometer can be hardly affected by external noise. Further, since the time width and the wind speed are represented by a square relationship, the effect of improving the accuracy of the wind speed measurement can be obtained.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a hot wire anemometer according to a first embodiment of the present invention.
FIG. 2 is a time chart showing the operation of the hot wire anemometer according to the first and second embodiments of the present invention.
3A is a graph showing a relationship between a time width and a wind speed according to a first embodiment, and FIG. 3B is a graph showing a relationship between a time width and a wind speed according to a second embodiment.
FIG. 4 is a block diagram showing a configuration of a hot wire anemometer according to a second embodiment of the present invention.
FIG. 5 is a block diagram showing an example of a conventional hot-wire anemometer.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Platinum wire 2 Bridge circuit 3 Feedback amplifier 4 Steady state determination circuit 5 Analog switch 6 Clock oscillator 7 Cable 8 Waveform shaping circuit 9 Time width detector 10, 21 Wind speed converter 11 Display 20 Discrimination circuit

Claims (2)

A bridge circuit including a heating wire serving as a sensor on one side;
A feedback amplifier that receives a voltage difference between both sides of the bridge circuit as input, and feeds back a differential amplified output to the bridge circuit;
Feedback current interrupting means for interrupting the output of the feedback amplifier at a constant cycle and adding to the bridge circuit;
Steady state determining means for outputting a pulse signal having a time width until the output becomes a steady state from the feedback amplifier,
Time width detection means for detecting the time width of the output from the steady state determination means,
A wind speed converting means for converting a signal of a time width obtained from the time width detecting means into a wind speed value. A bridge circuit including a heating wire serving as a sensor on one side;
A feedback amplifier that receives a voltage difference between both sides of the bridge circuit as input, and feeds back a differential amplified output to the bridge circuit;
Feedback current interrupting means for interrupting the output of the feedback amplifier at a constant cycle and adding to the bridge circuit;
Discriminating means for outputting a signal obtained by discriminating a signal obtained from the feedback amplifier at a predetermined level,
Time width detecting means for detecting the time width of the output from the discriminating means,
A wind speed converting means for converting a signal of a time width obtained from the time width detecting means into a wind speed value.

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